An implantable medical device (IMD) is implanted in a patient to monitor, among other things, electrical activity of a heart and to deliver appropriate electrical therapy, as required. Implantable medical devices include pacemakers, cardioverters, defibrillators, implantable cardioverter defibrillators (ICD), and the like. The electrical therapy produced by an IMD may include pacing pulses, cardioverting pulses, and/or defibrillator pulses to reverse arrhythmias (e.g., tachycardias and bradycardias) or to stimulate the contraction of cardiac tissue (e.g., cardiac pacing) to return the heart to its normal sinus rhythm.
Electrodes coupled to leads are implanted in the heart to sense the electrical activity of the heart and to deliver electrical therapy to the heart. The electrodes communicate the electrical activity as cardiac signals to the IMD via the leads. The electrodes may be placed within the chambers of the heart and/or secured to the heart by partially inserting the electrodes into the heart. The cardiac signals sensed by the electrodes are used by the IMD to deliver appropriate pacing therapy and/or stimulation pulses, or “shocks” to the heart.
A lead failure occurs when an electrode fails. The electrodes may fail and no longer be capable of accurately sensing and communicating cardiac signals to the IMD. Known lead failures involve electrodes fracturing, breaking or becoming dislodged from the myocardium. Lead failures can result in increased noise in the cardiac signals communicated to the IMD. With respect to fractured electrodes, the noise may be caused by the fractured components of the electrode rapidly making and breaking contact with one another at the fracture site. This type of noise may be referred to as chatter noise.
Lead failures can result in an IMD applying unnecessary or incorrect pacing or stimulation pulses to the heart. For example, if chatter noise occurs at a sufficiently high rate, the IMD may misclassify the rate of the chatter noise as a tachycardia or fibrillation, such as ventricular tachycardia (VT) or ventricular fibrillation (VF). The IMD may then erroneously apply pacing or stimulation pulses to the heart. Such unnecessary pacing and stimulation pulses can cause significant discomfort to patients.
Systems have been proposed to detect lead failures based on certain parameters such as differences in R to R intervals, high impedance, impedance trends and slew rate. However, prior detection systems do not identify which individual electrode(s) is associated with a lead failure. Nor do prior detection systems offer robust solutions to mitigate failures in sensing electrodes.
Early detection of lead failures and the locations of the lead failures is desired. Early detection and notification of a lead failure may enable the patient's physician to reconfigure the IMD to avoid using the failed electrode. Alternatively, the physician may otherwise adjust treatment of a patient until the failed lead can be replaced. Known methods of detecting lead failures may not accurately detect a location of the lead failure. That is, while the method may be able to determine that a lead failure has occurred, the methods do not provide the patient's physician with a location of the failure, such as an identification of the electrode on the lead that has failed.
A need exists for a method and system that identifies a potential lead failure in an IMD and the location of the failure. As the application of stimulation and pacing pulses to a patient's heart largely depends on the accurate sensing of cardiac signals, detecting failed leads may avoid continued sensing using the failed leads. Additionally, earlier detection of failed leads may permit physicians to reconfigure operation of the IMD to avoid continued use of the failed leads until the leads can be replaced.